Following are some acronyms used in this description:
BCH broadcast channel
CSG closed subscriber group
eNB evolved NodeB (base station)
E-UTRAN evolved UTRAN (3.9 G or LTE)
GERAN GSM EDGE radio access network
GSM global system for mobile communications
LTE long term evolution
MME mobility management entity
OFDM orthogonal frequency division multiple access
P-BCH primary BCH
PLMN public land mobile network
SU-1 scheduling unit 1 (system information)
TA tracking area
UTRAN UMTS terrestrial radio access network (3 G)
UE user equipment
WLAN wireless local area network
WCDMA wideband code division multiple access
Adjacent cell measurements are carried out in cell-based telecommunications systems. As known to those skilled in the art, the adjacent cell measurements are the basis for the handover and cell reselection decisions. The user equipment UE (mobile terminal), measures signal quality (such as signal strength, bit error rate BER, bit error probability BEP, or other signal quality parameters in use) from its serving cell and also from adjacent cells and reports these to the network in a measurement report. The measurement reports may be sent at regular intervals or in reply to a request/command from the network. The UE typically determines which cells are adjacent, and more narrowly which ones to measure, based on neighbor lists which in the prior art are delivered to the UEs on one or more control channels of the wireless system. The neighbor lists contain the necessary data about the adjacent cell so that the UE can find the neighbor cells easily and efficiently with reference to the list stored in its local memory.
In a large network with an extensive number of small cells, the process of determining the right or most appropriate neighbor to include in the neighbor lists that are used to configure the network is a substantial task. E-UTRAN (evolved universal mobile telecommunications system terrestrial radio access network, also known as 3.9G or long term evolution LTE) is developing to include more network cells than previous systems, including private networks (a single cell or group of cells) which E-UTRAN terms closed subscriber group CSG network cells with home eNBs (node B's or base stations). These are also known more generically as private networks, and are available for traffic (data and/or voice) only to those UEs specifically allowed access (e.g., registered as subscribers or guests) in the private network's subscriber group. Other wireless systems (GERAN, GSM, UTRAN, WCDMA, OFDM) are also proceeding in this general direction incrementally as more functionality is shifted from the radio network controller RNC to the base stations BSs. An individual private network may cover a relatively large geographic area with multiple cells (e.g., a corporate network or a large university campus), or may consist of a single home node B. Below, the term whitelist is used to refer to a list of private (CSG) cells for which a particular UE has access rights.
Relevant to these teachings is U.S. Provisional patent application No. 60/850,108, filed on Oct. 6, 2006 (now U.S. patent application Ser. No. 11/973,030 and International Patent Application No. PCT/IB07/02955 each of which was filed 4 Oct. 2007), describes that the UEs determine individually to limit their measurement reports based on certain criteria. U.S. Provisional patent application No. 60/881,287, filed on Jan. 18, 2007 (now U.S. patent application Ser. No. 12/009,399 and International Patent Application No. PCT/IB08/00104 filed respectively on 18 and 17 Jan. 2008), describes the network making decisions concerning the UE-generated measurement reports, which enables restricted requests for the mobile terminal to measure and report.
The closed subscriber group concept has been introduced is being standardized in E-UTRAN in 3GPP TS 36.300; Overall Description; Stage 2 (V8.1.0). CSG refers to a group of users which are given the rights to access a CSG cell. In other words, a CSG cell can only be accessed by UEs which belong to the CSG associated to that cell. These teachings relate to the UE measurement reporting aspects of the CSG concept.
The CSG layer refers to the layer formed by the CSG cells, and macro layer refers to the layer formed by the non-CSG cells (i.e. regular cells for which no CSG is defined). A CSG subnet refers to cells with continuous coverage associated to the same CSG.
Due to the large possible number of CSG cells under the coverage area of a macro (non-CSG) cell, and unlike with measurement reporting of non-CSG cells, measurement reporting of CSG cells cannot rely on physical layer identities identified by the primary and secondary synchronization channels P-SCH and S-SCH for unique identification of the target. Thus the UE's measurement report concerning CSG cells needs to include additional information for the network to uniquely identify the reported CSG cells.
Specifically, the network would need possibly to know:                CSG TA (eNodeB is aware of the whitelist TA, provided by the MME and should be part of the context transfer).        Identity of the cell in that TA        Other parameters such as measurement quantity are also needed. If one wants to be able to include non-allowed CSG cells into the measurement report, there is additionally a need for a CSG-group match indicator.        
This leads to several questions.
A) What Information to Include in a Measurement Report:
UEs without a CSG subscription would possibly be able to use a less complex measurement report. An open question is whether the UE without a CSG subscription should be allowed to skip any measurements on CSG cells, or should they also be able to report them. It is anticipated that there will be a strong demand from operators to also allow UEs without a CSG subscription to report CSG cells (e.g. for self optimising network purposes).
B) How to Uniquely Identify Cells (Who is Responsible—UE OR ENB):
Parameters are needed in order to uniquely identify a cell are listed above. As the TA itself is rather large and the TA whitelist is delivered by the network, it makes sense to use an indexing system when reporting instead of including the actual TA. If this is chosen it will naturally limit the UE without a CSG subscription to report CSG cells (and a similar restriction for CSG subscribers: only cells with TA included in the list can be reported) unless some other approach is taken.
C) Reporting for Self-Configuration:
UEs should be able to report CSG cells that are not included as part of its subscription. Based on this information it is useful for the operators to detect interferers and reallocate the physical cell identifier (PHY cell ID) of the CSG cells. This kind of reporting is not the default reporting though and should be restricted to optimization campaigns.
In summary, several problems have been identified:                What to report to identify a target CSG cell;        Inclusion of allowed/restricted CSG cells into measurement report;        Reporting of allowed CSG cells; and        Whether one measurement report format is suitable for all purposes or multiple formats are required.        
Several of these issues were addressed as the 3GPP TSG RAN WG2 meeting #59 held on Aug. 20-24, 2007 in Athens Greece, as detailed at documents R2-073307, R2-073684, R2-073374, R4-071263, R4-071451, and R4-0701494 (attached to the priority application as respective appendices A-F). What is needed is a standardized approach to cell measurements when a UE is in range of a private network cell but is not a member of that private network.